Grecian red mud — thickening and filtration parameters and process design

MUDTHICKENINGANDFILTRA

Grecian Red Mud - Thickening and Filtration Parameters and Process Design By N Leontaridis and D Marinas-Kouris

Department of Chemical Engineering, National Technical University of Athens, Athens, Greece. The behaviour of red mud in thickening and filtration tests has been studled for the purposes of calculating relevant parameters and of examining the possibility of designlng a suitable process for the thickening and flitratlon of this industrial by-product. Sedimentation experiments have been carried out with particle concentrations In the range of 190 - 440 g/l and with and without the use of floccuiants. A weak anionic floccuiant has been found to accelerate the sedimentation rate by a factor of two or three in ail cases. Constant pressure filtration experiments have been carried out in the pressure range 0- 730 mmHg. These tests have shown that: for filtration rates of 0.5 - 1.5 mg/mzha pressure over 230 mmHg is required; filtration rates accelerate with the use of a weak anionic fiocculant; the red mud cake can be considered Incompressible. On the basis of these results, the preliminary design of a red mud condensation process has been formulated. Bed mud is the main by-product of the Bayer bauxite process for the manufacture of aluminium. Treatment of bauxite ore in the Bayer process produces alumina and red mud. This residue has until recently been considered technologicallyuseless, although it is present in large amounts wherever the Bayer process is used. Approximately one ton of red mud is produced for each ton of alumina; the mud contains oxides of Fe, Al, Ca and Ti in more or less hydrated forms, as well as other minor elements which remain undissolved during the extraction operation of the Bayer process. Over the years, technical and patent literature has reported various schemes for the utilisation of red mud - as an ingredient in Portland cement, as a lightweight construction aggregate, and as pigment, filler, ceramic or colouring material after the removal of its sodium alkali-metal content. But a large-scale use of red mud does not yet exist. If its metal content could be extracted economically by some metallurgical process, it would become an enormous source of valuable materials and pollution caused by red mud would be reduced. At present, this waste mixture is usually pumped into the sea or into nearby terrestrial ravines, creating a great ecological problem. In Greece, for example, the waste is pu~~$~t~; the narrow Corinthian bay, destroying the The schekes for utilisation generally demand a reduction of the water content, using unit operation techniques, to produce a condensed material for further metallurgical or non-metallurgical use. Mechanical operations - like thickening and filtration - can be used as a first stage in removal of the water from the raw material. Thus, it is of interest to examine the scale and the equipment required for such a process in a preliminary design. Thickening of red mud Gravity sedimentation of a slurry appears to have an initial steady rate before it changes to reflect hindered settling.This initial rate is proportional to the square of the Stokes diameter of the particle and is given by the Stokes eqution~l~:

Flltmtl~n&Separatbn January/February

1992

ust =

& (ps - P) g

(1)

18n

in which ps and p denote the density of particles and liquid, respectively. Whenever there is a high concentration of particles in the slurry,however, hindered settling is observed from the beginning and the initial rate of sedimentation is consequently lower than that predicted by Eq.(l). The new value, u, is given by the following equationc2): +--=

(l-wj4.a

(2)

In this expression w is the mass fraction of the particles. The condition Na < 0.2 of laminar flow is necessary for Eq.(l) to be valid, so we can describe the sedimentation rate with the Stokes equation up to a certain size of the particles. The limit for red mud is 74 pm where there is sedimentationin water, and the density of the particles (p,) is 4.27 g/ml. Figure 1 presents the particle size distribution of Greek red mud. We can see that 86 % of the particles are

80 -

E

.e p

00

‘-

40-

*0 20 -

O-38 mkxo

3Q-b3 mlow W74mloro

74-140 mloro

140- mloro

Diameter (micrometre) Fig.1 ParUcle size dlstrlbution for a Greek red mud sample (QWMesh). 51

MUDTHICKENINGANDFILTRATION Particle concentration (g of solids/ litre) 190 300 440

Theoretlcal ExperImental w sedimentation sedimentation rate from Stokes rate (mhec) (mlsec) 0.12 0.26 0.40

17.73E-6 7.03E-6 2.65E-6

21.20E-6 9.62E-6 2.02G6

Table 1 Experimental and theoretical sedimentation rates.

under 74 pm and therefore satisfy the condition Nb c 0.2. We should also note that red mud appears as fine particles- 78 % are under 38 9.min diameter. lb remove through sedimentation every particle under 4 urn, the required settling rate - calculated from Stokes law - is 28.5E-6 m/set, and this rate becomes lower if there are more than 50 grammes of solids per litre. Table 1 compares the theoretically calculated sedimentation rates for various particle concentrations with the experimental sedimentation rates, which are also shown in Fig. 2. The divergence of 20 - 25 % is considered to be satisfactory,since there is no information for the particle size distribution under 38 pm. On the basis of the experimental values, we can conclude that there are fewer particles under 38 pm than would be expected if we used an extension of the Rosin-Rammler distribution line (I).It must be noted here that particles under 1 urn do not sedimentate because they are affected by Brownian motion; this limit goes up to 3 - 4 9m if there is a mixer in the slurry. The very slow sedimentation rates observed would demand a large uneconomic and slow-operating thickener. We therefore examined the use of flocculants to improve the thickening operation. For this purpose several commercial flocculants were tested. Most commercial flocculants are polyacrylamides of a high molecular weight. We tested four strong anionic flocculants, two weak anionic, and one neutral, with constant concentration of particles. Of these, two - one strong (Na81COQ)and one weak (Na-7862) - gave the highest sedimentation rates and the finest clarity and were tested further. Six different flocculant concentrations (5, 10, l&20,25, and 30 ppml were tested with three concentrationsof red mud particles (190,300, and 440 g solids/&e). Every test was repeated three times. The weak anionic flocculant (Na-7862) gave consis-

tently better resulta than the strong one (Na-81C09). Some of the results are presented in Figs. 3 & 4, which give the improved sedimentation rates for the two flocculants in various concentrations with the lowest concentration of red mud particles (190 g/I). Additional results are given in Fig. 5 for a flocculant concentration of 15 ppm and the highest concentration of particles (440 gill. The optimum concentration of the weak anionic flocculant (Na-78621,was found to be 25 ppm for red mud particle concentrations of 190 and 300 g/l, and 30 ppm for 440 g/l. No further improvement in the sedimentaI

I

--

+ 190 gr’solids/l +81C09,5ppm s 81CO9,lOppm 8 81 CO9,15 ppm * 81CO9,20 ppm + 81CO9,25 ppm i - 8lCO;,30ppm 1 ._ 0

160

loo

GO

200

Time (min) Fig.3 Results of thlckenlng test using the strong anionic flocoulant Na81ClW.

+ 7862,5 ppm __

_._I__- . --. I,( )

100

Time (min) Flg.4 Results of thlckenlng test using the wask ankmlc fl~ulant No-7882.

T

s

t J.._.__.~

Jt plus81COQ 15ppm I

2t

I 0

fJ0

100

lG0

I 200

lime (min) Flg,2Results of thickonlng W on rsd mud of three different sollds concentrations (190,300 and 440 g/l). 52

Flg.5 Thlckenlng tests on the hlghsst sollds contsnt rod mud, wlth and without the two flocculants. January/February

1992

FH~~~~oII 6 ~mtion

MUDTHICKENINGANDFILTRA Experimental Concentration concentration of flocculant sedimentation rate (m/se@ @pm) (g of solidwlltre) Particle

190 190 190 190 300 300 300 440 440 440 440

0

21.20E-6 50.63E-6 52.53E-6 52.52E-6 9.62E-6 17.43E-6 22.96E-6 2.02E-6 4.17E-6 6.67E-6 6.92E-6

:“5

30 0 15 25 0 15 3’:

Table 2 Experimental sedlmentatlon rates for the weak anionic flocculant.

tion rate was observed for flocculant concentrations higher than 30 ppm, (the tests in some cases reached 200 ppm). These results are in accordance with those of other investigators, and lead to the conclusion that the weak anionic polyacrylamides are suitable flocculants to speed up the thickening of red mud(3J). Table 2 presents experimental values of sedimentation rates for various concentrations of solids and using the weak anionic flocculant. The observed improvement, which is about 100 - 150 8 on the original rates, allows the use of a smaller thickener which operates with higher water overflow and so is more economical. Considering that the slurry settles until it reaches the compressionzone of the thickener (change of inclination in the TaJmoge- Fitch diugrurnY6~,we estimate that 40 % of the water content will be removed, producing red mud with 550 - 600 grammes of solids per litre. The exact value will depend on the initial concentration of particles and the particle size distribution. F’urther water removal will slow down the thickening operation, because a longer retention time would be required in the

applicable to another. This is because of the role of the nature and history of the solid particles and their interaction. A large number of small-scale filtration tests were performed using red mud which was the product of a previous thickening at 550g of solids per litre. The filtration device was relatively simple and operated under standard pressure. A small needle valve proved to he useful, permitting fine adjustment of the vacuum level. Great care was taken to assure that the test slurry was formed and handled in the same way that the production slurry will be. Slurry with 200 g of solids per litre was also used in the filtration tests to obtain more information about the material’sbehaviour. Eight different levels of pressure were tested between 0 and 730 ‘lbrr, and four concentrations of the flocculant (Na-7862) which gave the best results in the /

lr

--.

,aef_____~_.._;

0.1'

loo

I

L

2w

300

1

j,~

1

1

400

i

1

1

600

609

Volume (cm3) Fig. 6Resulte of flltratlon tests on red mud showing the Influence of pressure.

tank.

The condensed red mud has a density of 1.37 - 1.42 g/ml and can be pumped to a filter for further water removal. Flltratlon of red mud Filters that function at standard pressures are common in industry, especially where a continuous operation is taking place. Poiseuille’s equation can be integrated as follows for constant-pressure filtration, giving the relationship between the total time and filtrate measurements(?,W: dt nrcV I&, (31 -= -+dV A2P AP In this equation Srn is the resistance of the filter medium. The special resistance of the cake depends on the pressure and is given by (8.9): r = r,.Pe (41 The resistance of the filter medium, &, appears to have a small increase with pressure but is taken to be practically constant(*~~9). The theory of filtration is never used as the only basis for the design of a filter,but it remains valuable in interpreting laboratory tests, in finding optimum conditions, and in predicting the effects of changes in operation. The use of filtration theory is limited by the fact that filtering characteristicsmust be determined on the actual slurry in question. Data obtained on one slurry are not Ritratlon 81SsparsUonJanuary/February

1992

- ---+

200

+e dP = 230 mmHg

300

400

I

I

600

‘Boo

Volume (cmg Fig. 7 Results of filtration tests at different pressures. The results of Fig. 6 are replotted with a dlfferent vertical scale and the addltion of a reference line for P = 0 Tow.

z/

i=

8550gr S./lit10 ppm x 5jOgr Alit 15imm 55Ogf S./lit5 ppm i 8 550gr S./lit 0 ppm

o -&

0

60

loo

lb0

200

260

300

360

400

Volume (cm3) Fig. 8 EfM3 of flocculant concentration on the fWation of red mud. 52

MUDTHICKENINGANDFILTRATION

*

Particle concentration (g of solidsMe)

Flocculant concentration (ppm)

DP pressure (mmHg)

Experimental rates of filtration (mVm*.h)

200 200 200 200 200 550 550 550 550 550 550

:

320 580 728 320 580 130 280 580 280 280 580

1.053 - 0.400 1.287 - 0.591 1.388 - 0.870 1.248 - 0.585 1.403 - 0.888 0.488 - 0.292 0.557 - 0.329 0.815-0.382 0.583 - 0.330 0.853 - 0.417 1.243 - 0.550

0 lo* lo* 0 0” 5 * 1:*

preliminary tests. Every test was repeated 2 or 3 times. In Fig. 6 we can see the influence of pressure upon the tiltration rate for mud with 200 g of solids per litre. In Fig. 7 the line of P = 0 ‘Ibrr is added for the same mud, showing the improvement in filtration rates through the use of pressure. Figure 8 presents filtration rates using the anionic flocculant Na-7862 for mud with 550 gof solids per litre. The common practical rule, according to which one must use a flocculant of opposite polarity in the filtration from that in the thickening, is not valid. In the case of red mud, no improvement in the filtering rates was noticed with the use of cationic flocculants. From the same diagram it is obvious that the flocculant does not afYectthe special resistance of the cake, since the inclination of the filtration lines remains the same. In Table 3 one can see fdtration rates that were observed during tests under various conditions (the asterisk denotes that this concentration of flocculant gives the optimum rate for the given conditions). The formed cake in all cases contained 40 f 2 % wlw on a wet basis. The experimental filtration data, which show good consistency, can give us the special resistance of the red mud cake at various pressures (inclination of the lines in Figs, 6 & 7), through a parameter estimation on the linear model of Eq.(3). The same operation with Eq.(4) predicts the cake’s compressibility, s, which is found to be 0.X-0.26 for solids concentrations in the range 200 - 600 g/I. The range of s for compressible particles is 0.80 - 1.00; incompressible particles, like sand, have

2.OOE*lO I 3cQOo

:

1

i~~1lII 3ocuDo

Pressure (Pa) Fig. OEfhct

of

pres6ura on the compreeeibllity mud cake.

54

of

red

Table 3 Experimental tlltratlon rates. (asterisks denote optimum flocculant concentration for given conditions).

the limit value of s = 0. The red mud cake is therefore considered to be incompressible. Figure 9 presents the resistance of the cake with respect to pressure, for a red mud sample of 200 g of ;olltIr litre which appears to have a compressibility .

.

Thickener and filter design The thickening and filtering test results were employed for a preliminary design of the process. The process involves a thickener and a filter, both operating for the enrichment of red mud. The raw material for the process, the red mud, is the by-product of the last alkali recovery tank of the Bayer process. A fresh feed of red mud with 300 - 350 g of solids per litre is the input to a bottom mixer sedimentation tank. Through this process, 40 % of the water content is removed, providing a condensed red mud with 650-600 g/l. The required cross-sectional area of the sedimentation tank is given by the following equation’? A F-D E(5) Pu,

in which F and D are the amounts of water (kg per kg of dry solids) in the feed and in the sedimented slurry, respectively. The initial sedimentation rates were obtained from the sedimentation tests for various particle and flocculant concentrations. In Fig. 10 values are given for the required thickener area, with respect to the different particle concentrations of the feed. The second curve

p1 ioo

u

160

200

2bO

300

360

400

4bO

6Cil

Concentration of solids (gr.solid/litre)

Fig.10A dealgn chart which shows how the cros+eeWonal area required for the thlckoner varlw wlth solids concentration and how lt Is Influenced by the use of a flocoulant. January/February 1992 FlitmUon & Sepemtlon

*

refers to rates measured using the anionic flocculant in its optimum concentration, as shown in Table 2. Calculation determines that the required area of the thickener is 0.064 mz/kg solids/b without the use of flocculant, and 0.019 m2/kgsolids/b with the optimum concentration of flocculant Na-7862 (25 ppm), for,red mud of 300 g of solids per litre. The filtration rates are found to be 0.85 - 0.42 mYm*.h with the use of the optimum flocculant (15 ppm Na-7862) and 0.56 - 0.33 m9/m2h without the flocculant. These values were calculated for red mud with 550g of solid per litre and a ftitration pressure of 260 ‘Ibrr (Table 3). The use of higher pressures can be examined in accordance with the process economics. At present, P is considered to be a design variable, with a value of 260 lbrr. The size of the equipment required can be calculate& consider a base production of 500 000 tons/year of red

Red mud SO0000 t/year 7w”h wet basis

3OOBOO~ear

-

-50% wet basis Fbaxhnt

I

I

CA

W&r 50 000 Vyear

Water 2OO;OOO t/year Flg. 11 Schemstlc

ofthlckener

and filter unit for red mud.

ttltchner

MUDTHICKENING ANDFILTRATION mud with a concentration of 350 g/l which has 70 % w/w moisture on a wet basis. In this case the required area of the thickener is 1000 ma without the use of flocculant, and 300 m* with the use of the optimum flocculant concentration. Using a safety factor of 0.25, the thickener’s height is 3 m, while the feeding zone is 1 m. The water overtlows with a rate of 20 m9/b, and the mud collection equipment, which is based on a hypernatent bridge, removes the sludge with a rate of 3r5t/h. The sludge is collected at the centre of the sedimentation tank with the help of branches which have a slow rotation of 0.06 rpm (about 10 cm/set peripheral velocity). The filter is of the vacuum rotary type, considered to be economic for large filtration processes, and operates under 260 Ibrr relative pressure. The feed to the filter is the outflow of the thickener, that is, 300 000 tons/year of red mud with 50 % moisture on a wet basis. The filtrate is drained from the 20 m2 of the drum with a rate of 5 t/b. If we use the Na-7862 flocculant as a filter aid, the drum area becomes 15 m2.This is a middle size vacuum rotary filter (the large ones have a drum area of 30 m2(Y. About 256000 tons/year of red mud cake would be scraped off the filter drum with 40 % w/w moisture on a wet basis. In Fig. 11 one can see the entire process. Fig. 12 is a pie chart which shows the quantities of water that are removed from the red mud during the thickening and filtration steps. According to our experimental results, the processing method described above has been proved suitable for application on a large industrial scale; on the basis of laboratory tests, the manner in which the technological procedure could be planned for industrial purposes, has been shown. Conclusions An economic solution has to be found for the disposal of red mud. Aside from the environmental problem involved, valuable ingredients are wasted by throwing away this aluminium by-product. Mechanical operations - thickening and filtering - can remove 80 % of the water content, which is the major problem in the utilization of the red mud. The use of flocculants and filter aids during thickening and filtration decrease the size of the process equipment required, thus reducing the cost. The condensed red mud, retaining only 20 % of the initial water content, can easily be dried with the use of a conventional dryer or, alternatively a solar unit. The results of filtration and thickening tests on Greek red mud can form a database for further process design, aiming at industrial use, because they reveal for the first time the material’s behaviour under various conditions. Nomenclature

ust velocity, referred to Stokes diameter

Pig. 12 PI0 chsrt showing the quentities of wster thet are removed from the red mud during thlckenlng and flltrstion step8,onthebssl8ottrestlng5OOOOOtonsofmudlnayesr. PWstlon & &pemtlon

January/February 1992

dSt Stokes diameter PS density of particles density of liquid gravitational acceleration : n viscosity mass fraction : time V volume of filtrate r special resistance of the cake solid particles per volume in the cake L cross sectional area P relative pressure r. constant of Eq.(4)

*

L u, F

b

MUD THICKENING AND FILTRATION compressibility of cake resistance of the filter medium initial sedimentation velocity kg water feeding/kg dry solids kjj water of sedi~e&atGd slurry/kg dry solids References

;I; ?Y”’ (4

1. McCabe, W. and Smith, J. Unit operations of Chemical Engineering, Second Ed., McGraw-Hill, 1976. 2. Co&on, J. and Richardson, J. Chemical Engineering, Vol. 2 Pergamon Press, 1966. 3. Kontopoulos, A., Statheli, A. and Svertleva, L, Perspectives for the Utilizatiop of Bed Mud - A Literature Survey. Z%c. i$76%ngr. of Maneml Wealthof Greece, TEE Athens, May

4. Kontopoulos, A., chrysaoulakis,

J., veesiliou, P., MarimsKouris, D. and Vrett+, P. Physical, Chemical and Mineralogical Characteristm of the Grecian Bad Mud. Pm. 4th Znt. Congr. for the Study of Bauxitzu, Aluminu and AZuminium, Athena 1978. 5. KontopouIos, A., Marinos-Kouris, D. and Vassiliou, P. Ef&ct of I%cculents on bttling and Filtration of Red Mud in the Alumina Industry. ZMtmtbn & Sepwdon, Vol. te, No. 4, July/August 1981, pp 321-322. 6. F’itch, B: curfent Theory yd Thickener Design: Parts 1.2, ;n53 Fzltmtwn dt Sepratwn, JtiAug, SepWOct, NovDec 7.

$$as,

8.

Ives,‘K. The Scienti~?~Basis of Fiitmtion, Noordhoff-Leyden @mand~, 1976. Schweitzer, P. A. Filtration, Sections 4.1-4.4 in Handbook of &par&ion Prvceas lkchniques for Chemical Engineers, McGraw-Hill, New York, 1979.

g.

D. Zndustriul ZWration of Liquids. Leonard Hi&

January/February 1992

Rltntlon & &pmHlon

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caract&isation et le contr6/e de qua/it6 tent des HEPA que des tiltres d gaz. On a d6veiopp8 un test commun et on a construit deux diff&entes unit& d’essai. En mesurant slmultan6ment la p&&ration partieiie et /a perte de charge, des Etudes de charge peuvent &Ire faites dans un laps de temps de seulement quelques minutes. Des mesures sous conditions varibas ont montr4 /‘influence de la vitasse faciab, de la concentration an amonf, de /a nature des poussi&es, du matdriau filtrant et de la

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q51

discuten /as penetraciones y caides de presi6n dependientes de tiempo y tamado. con Libras electret y de vidrio y con medios de papel. (6 pdgs., 10 figs.,2 tabs., 8 rels)

Grecian Red Mud-Thlckenlng and Flltratlon Parameters and Prccer Dealgn Grlechlscher Rotschlamm-Elndkkund Flltratlonsparameter sowle ProzeBplanung vole N Leontaridis und D Marinas-Kinks

Est ist das Verhalten van Rotschlamm bei Endick- und Filtrationsversuchen studiert worden, urn die relevanten Parameter barechnen und die Mdglichkeit untersuchen zu kbnnen, ein geaignetes Verfahren zum Eindlcken und zur Filtration dieses industrial/en Nebenprodukts zu entwickeln. Es sind Sedimentierexperimente mit Partikelkonzentrationen im BereIch van 19044Ogli sowohl mit a/s such ohne Beimengung van Flockungsm~tteln durchgetiihrt worden. Man hat ein schwaches aniomsches Flockungsmittel gefunden, das die Sedimentationsratein a//en Fdllen urn em ZweC

oder Dreifaches beschleuni t. AuBerdem sind Gleichdruck-Filtrations-Experimente in eir Drockbereic? vqn 8- 730mmHg durchgef’hrt worden. Diese Tests habe fol endas gazargt’ fur FUtratronsratan van OS-l.5 s lm’h 1st ein Druck van mehr a/s 23 mmHg erforderlich; Filtrationsgeschwindigkeiten nehmen bei Beimengung eines schwachen anionischen Flockungsmittels zu; der Rotschlammkuchen 1st ais inkompressibelzu betrachten. Auf der Basis dieser Ergebnisse ist die vorlfiufige Form eines Rotschlamm-Kondensationsverfahrens entwickelt worden@ sn., 12 abb., 3 tab., 9 ret)

Bouea rouges grecquea-Epalulssement, param&trea de flltratlon et conception d’un pro&d6 de traltement par N Leontarid&~ et D Marinas-Kou?+s Le comportement des boues rouges dans des essa!s d’dpaississement et de filtration a 618 Btudi6 dans /e but de calculer /es param&res op&atoires et d’examinar la possibilit.4 de concevoir un pro&d& convenable pourl%paississament et la filtration de ce sous-produit industriel. Des experiences de &d!mantation ont 6th conduites avec des concentrations en solide variant entre 790 et 440 g/l sans et avec flocuients. On a trouti qu’un tlocuiant doux anionique acc&&a!t /a vifesse de ddcantation par un facteur deux ou trois dens tous !es cas. Des essars de filtration CI pression constante Barro rojo de procedencla grlega -espeaadura,

ont bgalement 616 men& dans vne piage c$e0 730 mmHg. Ces essais ont montr+ que pour des vitesses de filtration de 0.5 d 1.5 m I d h. il faut utiliser una pression supeneure B 23OmmHg les vitessesde filtration s’accroissent lors de l’emploi d’un flocutant doux anionique; /es boues rouges peuvent Btre consid&des comme incompressible% sur base de ces r&ultafs, on a pu formuler I’avant-projat d’un pro&d6 de traitemant des boues rouges. (6 p.. 12 fig.. 3 tab., 9 r&)

par&metros de flltracldn, y dlsaiio de proceao

por N Leon&rid&z y D Marinas-Kouv+s

y

Se he estudiado el comportamiento de barro rojo en pruebas de espesar y fitirar, para calcular pa&metros pertinentas y pars determiner /a posibilidad de disehar proceso para esta subproducto industrial. Experimentos de sedimentaci6n se han real&ado con concentraciones de pa&u/as en /a gama de 19040 II y con sin el empleo de agentes de Iloculaci6n. Se ha hallado que on egente 8:lolo aumenta el raz6n de sedimentaci6n por un factor de dos 6 tres en todos cases. Filtraci6n a presi6n constante en /a game de pretines de O-730 mmHg ha demostrado: para razones de

tzl 57

filtraci6n de 0.5-1.5 mslmsh es necesario una presidn de mas de 230 mmHg; razones filtracidn se aceleran con el empleo de agentes de Iloculaci6n Hojos anibnicor puede considerar incompresible/a torta de barro rojo. A base da estos resultados ha formulado diseho prekminar de un proceso de condensacidn para barro rojo. pBgs., 12 figs., 3 tabs., 9 Ref)

de se se (6

Emplrlcal Mcdelllng of a Dewaterlng Process ualng Multlvarlate Dab Analysis Emplrlsche Modellblldung sines Entwiiaserungaverfahrena unter Anwendung der mehrdlmenalonalen Datenanalyae van Ban& Her&h, Chris&r Albano, Alrik Ant&la zlnd Ben@ F&k4

Es wird eine Methoda baschriaben. mit der das Verhtiltnis zwfschen Betnebsverdnderlichen und Entwiisserungsparametern van Thunes-Scheibenfiltern unter Verwendung empirischer mathematischar Model/e in der LKAB-‘Pelletisieranlage’ bei Malmberget in Schweden untarsucht wird. Es wurde ein fast orthogonales Experimentierprinzip angewandt a//e unabh(ingigen VerCinderlk?hen durften ihre Varianten durchlaofen und waren in Pseudo-ZulaQfoge iiber die Experimente varteilt. Die Entw#sserungsparsmeter hlngen van zahlreichen VerBnderhchen ab, und anste/le eines Mcdillratlon

traditionellen mechanistischen Mode//s wurde ein empirisches Mode/l mit mehrdimensionaler Datenanafyse gewtihlt.Die Verhfiltnissesind in form van Regressionskoeffizienten ausgedriickt, die sich aos partieller Regression dar kleinsten quadrate ergaben. Es entstanden zwei empirische Mode//e. Die Model/e wurden ausgewertet, und auf exparimentellem Wege wurden die Parameter mit den Konstruktionsverdinderlichen in ein Verhdttnis gesetzt. Banutzerfreundliche Oberfi&hen-Methodik diante zur Ermitdung optimaler Bedingungen. e sn., 12 abb.. 5 tab., 10 ret)

emplrlque d’un pro&d6 de d6ahydratatlon utlllsant I’analyae multlvarlable par Ban&z Hem&

Christer Albano,

On d&M one mdthode pour relief /es varfebles op&atoses

et /es param&res de 6shydratation des tiltres B disques Thunes. dans I’usme de pellehsarron B LKAB B fi almberget en S&de, et ceia grBce B des mod&es math6mabques empiriques. On a utili& un schema exp&imental A peu pres orthogonal: routes /es variables indbpandantes ont pu parcourir leur domeine de vsriabon et BtaienfdistribuCs parmi /es exp6riences de tapon pseudoal8atoire. Les param&res de d&hydratabon dependent de plusieurs variables et un mod&e empinque base sur une analyse

Alrik Ant&la et Bengt Flykt

multivariable a 61.4choisi p/u?& qu’un mod&/e mkanistique traditionnel. Les relations sent exprim6es par des coefticients de r6gression obtenus par regression partieile des moindres car&s. Deux mod&es empiriquasont BtB conpus. Les mod&es ont 616 valid& et ias param&res ont 616 reti& aux variables do pro&d6 par l’extirience. Une m&hodobgie conviviale a 618 uti/i&e pour determiner /es conditions optimeles. (9 p.. 12 fig., 5 tab., 10 &I.)

Modelo empirko de un procero de deahldmtacl6n empleando anlllals de dator multlvarlablea par Ban& Hen&, Christer Albano, Alrik AntMa y Bengt FlyM Se describe m&odo de establecer relaci6n entre variables de opera&n

y parkmetros de deshidrataci6n de liltros de disco Thunes. en 18 planta LKAB (de hater bolites) de Malmberget. SuBcia. con modelos empiricos matem&icos. Se ha empleado disefio matem&ico casi ortogonal; todas /as variables independientes podian ebarcar la game de variaci6n y distribuirse entre /OS axperrmentos da manera seudoaleatoria. Loa pa&metros de deshidratacidn dependian de muchas variables, y se he escog!do un mode/o empiric0 a base de an&isis de datos multivariables antes que un modelo mecdnico traditional. Las relaciones se expresan por coehcrenres de regresidn 44

derivados de una regresi6n partial de 10s menos cuadrados. Se han prasentado. dos mode& empiricos. /OS cue/es se han validado, y se hen reiacionada /OS pa&metros con /es variables de disefio por experimentacidn. Se ha empieado metodoto ia lacil de usar, de reacci6n de superficies,pare determinar/as condicionesoptimas. 1 pdgs.. 12 figs., 5 tabs., 10 rets.)

January/February

1992

Flltratlon & Sepamtlon